/*
 * Copyright 2001-2004 Unicode, Inc.
 *
 * Disclaimer
 *
 * This source code is provided as is by Unicode, Inc. No claims are
 * made as to fitness for any particular purpose. No warranties of any
 * kind are expressed or implied. The recipient agrees to determine
 * applicability of information provided. If this file has been
 * purchased on magnetic or optical media from Unicode, Inc., the
 * sole remedy for any claim will be exchange of defective media
 * within 90 days of receipt.
 *
 * Limitations on Rights to Redistribute This Code
 *
 * Unicode, Inc. hereby grants the right to freely use the information
 * supplied in this file in the creation of products supporting the
 * Unicode Standard, and to make copies of this file in any form
 * for internal or external distribution as long as this notice
 * remains attached.
 */

/* ---------------------------------------------------------------------

	Conversions between UTF32, UTF-16, and UTF-8. Source code file.
	Author: Mark E. Davis, 1994.
	Rev History: Rick McGowan, fixes & updates May 2001.
	Sept 2001: fixed const & error conditions per
	mods suggested by S. Parent & A. Lillich.
	June 2002: Tim Dodd added detection and handling of incomplete
	source sequences, enhanced error detection, added casts
	to eliminate compiler warnings.
	July 2003: slight mods to back out aggressive FFFE detection.
	Jan 2004: updated switches in from-UTF8 conversions.
	Oct 2004: updated to use UNI_MAX_LEGAL_UTF32 in UTF-32 conversions.

	See the header file "ConvertUTF.h" for complete documentation.

	------------------------------------------------------------------------ */

#include "behaviac/base/convertutf.h"
#ifdef CVTUTF_DEBUG
#include <stdio.h>
#endif

static const int halfShift = 10; /* used for shifting by 10 bits */

static const UTF32 halfBase = 0x0010000UL;
static const UTF32 halfMask = 0x3FFUL;

#define UNI_SUR_HIGH_START  (UTF32)0xD800
#define UNI_SUR_HIGH_END    (UTF32)0xDBFF
#define UNI_SUR_LOW_START   (UTF32)0xDC00
#define UNI_SUR_LOW_END     (UTF32)0xDFFF
#define false	   0
#define true	    1

namespace behaviac
{
	/* --------------------------------------------------------------------- */

	ConversionResult ConvertUTF32toUTF16(
		const UTF32** sourceStart, const UTF32* sourceEnd,
		UTF16** targetStart, UTF16* targetEnd, ConversionFlags flags)
	{
		ConversionResult result = conversionOK;
		const UTF32* source = *sourceStart;
		UTF16* target = *targetStart;

		while (source < sourceEnd)
		{
			UTF32 ch;

			if (target >= targetEnd)
			{
				result = targetExhausted;
				break;
			}

			ch = *source++;

			if (ch <= UNI_MAX_BMP)   /* Target is a character <= 0xFFFF */
			{
				/* UTF-16 surrogate values are illegal in UTF-32; 0xffff or 0xfffe are both reserved values */
				if (ch >= UNI_SUR_HIGH_START && ch <= UNI_SUR_LOW_END)
				{
					if (flags == strictConversion)
					{
						--source; /* return to the illegal value itself */
						result = sourceIllegal;
						break;

					}
					else
					{
						*target++ = UNI_REPLACEMENT_CHAR;
					}
				}
				else
				{
					*target++ = (UTF16)ch; /* normal case */
				}
			}
			else if (ch > UNI_MAX_LEGAL_UTF32)
			{
				if (flags == strictConversion)
				{
					result = sourceIllegal;

				}
				else
				{
					*target++ = UNI_REPLACEMENT_CHAR;
				}
			}
			else
			{
				/* target is a character in range 0xFFFF - 0x10FFFF. */
				if (target + 1 >= targetEnd)
				{
					--source; /* Back up source pointer! */
					result = targetExhausted;
					break;
				}

				ch -= halfBase;
				*target++ = (UTF16)((ch >> halfShift) + UNI_SUR_HIGH_START);
				*target++ = (UTF16)((ch & halfMask) + UNI_SUR_LOW_START);
			}
		}

		*sourceStart = source;
		*targetStart = target;
		return result;
	}

	/* --------------------------------------------------------------------- */

	ConversionResult ConvertUTF16toUTF32(
		const UTF16** sourceStart, const UTF16* sourceEnd,
		UTF32** targetStart, UTF32* targetEnd, ConversionFlags flags)
	{
		ConversionResult result = conversionOK;
		const UTF16* source = *sourceStart;
		UTF32* target = *targetStart;
		UTF32 ch, ch2;

		while (source < sourceEnd)
		{
			const UTF16* oldSource = source; /*  In case we have to back up because of target overflow. */
			ch = *source++;

			/* If we have a surrogate pair, convert to UTF32 first. */
			if (ch >= UNI_SUR_HIGH_START && ch <= UNI_SUR_HIGH_END)
			{
				/* If the 16 bits following the high surrogate are in the source buffer... */
				if (source < sourceEnd)
				{
					ch2 = *source;

					/* If it's a low surrogate, convert to UTF32. */
					if (ch2 >= UNI_SUR_LOW_START && ch2 <= UNI_SUR_LOW_END)
					{
						ch = ((ch - UNI_SUR_HIGH_START) << halfShift)
							+ (ch2 - UNI_SUR_LOW_START) + halfBase;
						++source;

					}
					else if (flags == strictConversion)     /* it's an unpaired high surrogate */
					{
						--source; /* return to the illegal value itself */
						result = sourceIllegal;
						break;
					}
				}
				else     /* We don't have the 16 bits following the high surrogate. */
				{
					--source; /* return to the high surrogate */
					result = sourceExhausted;
					break;
				}
			}
			else if (flags == strictConversion)
			{
				/* UTF-16 surrogate values are illegal in UTF-32 */
				if (ch >= UNI_SUR_LOW_START && ch <= UNI_SUR_LOW_END)
				{
					--source; /* return to the illegal value itself */
					result = sourceIllegal;
					break;
				}
			}

			if (target >= targetEnd)
			{
				source = oldSource; /* Back up source pointer! */
				result = targetExhausted;
				break;
			}

			*target++ = ch;
		}

		*sourceStart = source;
		*targetStart = target;
#ifdef CVTUTF_DEBUG

		if (result == sourceIllegal)
		{
			fprintf(stderr, "ConvertUTF16toUTF32 illegal seq 0x%04x,%04x\n", ch, ch2);
			fflush(stderr);
		}

#endif
		return result;
	}

	/* --------------------------------------------------------------------- */

	/*
	 * Index into the table below with the first byte of a UTF-8 sequence to
	 * get the number of trailing bytes that are supposed to follow it.
	 * Note that *legal* UTF-8 values can't have 4 or 5-bytes. The table is
	 * left as-is for anyone who may want to do such conversion, which was
	 * allowed in earlier algorithms.
	 */
	static const char trailingBytesForUTF8[256] =
	{
		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
		1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
		2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5
	};

	/*
	 * Magic values subtracted from a buffer value during UTF8 conversion.
	 * This table contains as many values as there might be trailing bytes
	 * in a UTF-8 sequence.
	 */
	static const UTF32 offsetsFromUTF8[6] = { 0x00000000UL, 0x00003080UL, 0x000E2080UL,
		0x03C82080UL, 0xFA082080UL, 0x82082080UL
	};

	/*
	 * Once the bits are split out into bytes of UTF-8, this is a mask OR-ed
	 * into the first byte, depending on how many bytes follow.  There are
	 * as many entries in this table as there are UTF-8 sequence types.
	 * (I.e., one byte sequence, two byte... etc.). Remember that sequencs
	 * for *legal* UTF-8 will be 4 or fewer bytes total.
	 */
	static const UTF8 firstByteMark[7] = { 0x00, 0x00, 0xC0, 0xE0, 0xF0, 0xF8, 0xFC };

	/* --------------------------------------------------------------------- */

	/* The interface converts a whole buffer to avoid function-call overhead.
	 * Constants have been gathered. Loops & conditionals have been removed as
	 * much as possible for efficiency, in favor of drop-through switches.
	 * (See "Note A" at the bottom of the file for equivalent code.)
	 * If your compiler supports it, the "isLegalUTF8" call can be turned
	 * into an inline function.
	 */

	/* --------------------------------------------------------------------- */

	ConversionResult ConvertUTF16toUTF8(
		const UTF16** sourceStart, const UTF16* sourceEnd,
		UTF8** targetStart, UTF8* targetEnd, ConversionFlags flags)
	{
		ConversionResult result = conversionOK;
		const UTF16* source = *sourceStart;
		UTF8* target = *targetStart;

		while (source < sourceEnd)
		{
			UTF32 ch;
			unsigned short bytesToWrite = 0;
			const UTF32 byteMask = 0xBF;
			const UTF32 byteMark = 0x80;
			const UTF16* oldSource = source; /* In case we have to back up because of target overflow. */
			ch = *source++;

			/* If we have a surrogate pair, convert to UTF32 first. */
			if (ch >= UNI_SUR_HIGH_START && ch <= UNI_SUR_HIGH_END)
			{
				/* If the 16 bits following the high surrogate are in the source buffer... */
				if (source < sourceEnd)
				{
					UTF32 ch2 = *source;

					/* If it's a low surrogate, convert to UTF32. */
					if (ch2 >= UNI_SUR_LOW_START && ch2 <= UNI_SUR_LOW_END)
					{
						ch = ((ch - UNI_SUR_HIGH_START) << halfShift)
							+ (ch2 - UNI_SUR_LOW_START) + halfBase;
						++source;

					}
					else if (flags == strictConversion)     /* it's an unpaired high surrogate */
					{
						--source; /* return to the illegal value itself */
						result = sourceIllegal;
						break;
					}
				}
				else     /* We don't have the 16 bits following the high surrogate. */
				{
					--source; /* return to the high surrogate */
					result = sourceExhausted;
					break;
				}
			}
			else if (flags == strictConversion)
			{
				/* UTF-16 surrogate values are illegal in UTF-32 */
				if (ch >= UNI_SUR_LOW_START && ch <= UNI_SUR_LOW_END)
				{
					--source; /* return to the illegal value itself */
					result = sourceIllegal;
					break;
				}
			}

			/* Figure out how many bytes the result will require */
			if (ch < (UTF32)0x80)
			{
				bytesToWrite = 1;

			}
			else if (ch < (UTF32)0x800)
			{
				bytesToWrite = 2;

			}
			else if (ch < (UTF32)0x10000)
			{
				bytesToWrite = 3;

			}
			else if (ch < (UTF32)0x110000)
			{
				bytesToWrite = 4;

			}
			else
			{
				bytesToWrite = 3;
				ch = UNI_REPLACEMENT_CHAR;
			}

			target += bytesToWrite;

			if (target > targetEnd)
			{
				source = oldSource; /* Back up source pointer! */
				target -= bytesToWrite;
				result = targetExhausted;
				break;
			}

			switch (bytesToWrite)   /* note: everything falls through. */
			{
			case 4:
				*--target = (UTF8)((ch | byteMark) & byteMask);
				ch >>= 6;

			case 3:
				*--target = (UTF8)((ch | byteMark) & byteMask);
				ch >>= 6;

			case 2:
				*--target = (UTF8)((ch | byteMark) & byteMask);
				ch >>= 6;

			case 1:
				*--target = (UTF8)(ch | firstByteMark[bytesToWrite]);
			}

			target += bytesToWrite;
		}

		*sourceStart = source;
		*targetStart = target;
		return result;
	}

	/* --------------------------------------------------------------------- */

	/*
	 * Utility routine to tell whether a sequence of bytes is legal UTF-8.
	 * This must be called with the length pre-determined by the first byte.
	 * If not calling this from ConvertUTF8to*, then the length can be set by:
	 *  length = trailingBytesForUTF8[*source]+1;
	 * and the sequence is illegal right away if there aren't that many bytes
	 * available.
	 * If presented with a length > 4, this returns false.  The Unicode
	 * definition of UTF-8 goes up to 4-byte sequences.
	 */

	static UTFBoolean isLegalUTF8(const UTF8* source, int length)
	{
		UTF8 a;
		const UTF8* srcptr = source + length;

		switch (length)
		{
		default:
			return false;

			/* Everything else falls through when "true"... */
		case 4:
			if ((a = (*--srcptr)) < 0x80 || a > 0xBF)
			{
				return false;
			}

		case 3:
			if ((a = (*--srcptr)) < 0x80 || a > 0xBF)
			{
				return false;
			}

		case 2:
			if ((a = (*--srcptr)) > 0xBF)
			{
				return false;
			}

			switch (*source)
			{
				/* no fall-through in this inner switch */
			case 0xE0:
				if (a < 0xA0)
				{
					return false;
				}

				break;

			case 0xED:
				if (a > 0x9F)
				{
					return false;
				}

				break;

			case 0xF0:
				if (a < 0x90)
				{
					return false;
				}

				break;

			case 0xF4:
				if (a > 0x8F)
				{
					return false;
				}

				break;

			default:
				if (a < 0x80)
				{
					return false;
				}
			}

		case 1:
			if (*source >= 0x80 && *source < 0xC2)
			{
				return false;
			}
		}

		if (*source > 0xF4)
		{
			return false;
		}

		return true;
	}

	/* --------------------------------------------------------------------- */

	/*
	 * Exported function to return whether a UTF-8 sequence is legal or not.
	 * This is not used here; it's just exported.
	 */
	UTFBoolean isLegalUTF8Sequence(const UTF8* source, const UTF8* sourceEnd)
	{
		int length = trailingBytesForUTF8[*source] + 1;

		if (source + length > sourceEnd)
		{
			return false;
		}

		return isLegalUTF8(source, length);
	}

	/* --------------------------------------------------------------------- */

	ConversionResult ConvertUTF8toUTF16(
		const UTF8** sourceStart, const UTF8* sourceEnd,
		UTF16** targetStart, UTF16* targetEnd, ConversionFlags flags)
	{
		ConversionResult result = conversionOK;
		const UTF8* source = *sourceStart;
		UTF16* target = *targetStart;

		while (source < sourceEnd)
		{
			UTF32 ch = 0;
			unsigned short extraBytesToRead = trailingBytesForUTF8[*source];

			if (source + extraBytesToRead >= sourceEnd)
			{
				result = sourceExhausted;
				break;
			}

			/* Do this check whether lenient or strict */
			if (!isLegalUTF8(source, extraBytesToRead + 1))
			{
				result = sourceIllegal;
				break;
			}

			/*
			 * The cases all fall through. See "Note A" below.
			 */
			switch (extraBytesToRead)
			{
			case 5:
				ch += *source++;
				ch <<= 6; /* remember, illegal UTF-8 */

			case 4:
				ch += *source++;
				ch <<= 6; /* remember, illegal UTF-8 */

			case 3:
				ch += *source++;
				ch <<= 6;

			case 2:
				ch += *source++;
				ch <<= 6;

			case 1:
				ch += *source++;
				ch <<= 6;

			case 0:
				ch += *source++;
			}

			ch -= offsetsFromUTF8[extraBytesToRead];

			if (target >= targetEnd)
			{
				source -= (extraBytesToRead + 1); /* Back up source pointer! */
				result = targetExhausted;
				break;
			}

			if (ch <= UNI_MAX_BMP)   /* Target is a character <= 0xFFFF */
			{
				/* UTF-16 surrogate values are illegal in UTF-32 */
				if (ch >= UNI_SUR_HIGH_START && ch <= UNI_SUR_LOW_END)
				{
					if (flags == strictConversion)
					{
						source -= (extraBytesToRead + 1); /* return to the illegal value itself */
						result = sourceIllegal;
						break;

					}
					else
					{
						*target++ = UNI_REPLACEMENT_CHAR;
					}
				}
				else
				{
					*target++ = (UTF16)ch; /* normal case */
				}
			}
			else if (ch > UNI_MAX_UTF16)
			{
				if (flags == strictConversion)
				{
					result = sourceIllegal;
					source -= (extraBytesToRead + 1); /* return to the start */
					break; /* Bail out; shouldn't continue */

				}
				else
				{
					*target++ = UNI_REPLACEMENT_CHAR;
				}
			}
			else
			{
				/* target is a character in range 0xFFFF - 0x10FFFF. */
				if (target + 1 >= targetEnd)
				{
					source -= (extraBytesToRead + 1); /* Back up source pointer! */
					result = targetExhausted;
					break;
				}

				ch -= halfBase;
				*target++ = (UTF16)((ch >> halfShift) + UNI_SUR_HIGH_START);
				*target++ = (UTF16)((ch & halfMask) + UNI_SUR_LOW_START);
			}
		}

		*sourceStart = source;
		*targetStart = target;
		return result;
	}

	/* --------------------------------------------------------------------- */

	ConversionResult ConvertUTF32toUTF8(
		const UTF32** sourceStart, const UTF32* sourceEnd,
		UTF8** targetStart, UTF8* targetEnd, ConversionFlags flags)
	{
		ConversionResult result = conversionOK;
		const UTF32* source = *sourceStart;
		UTF8* target = *targetStart;

		while (source < sourceEnd)
		{
			UTF32 ch;
			unsigned short bytesToWrite = 0;
			const UTF32 byteMask = 0xBF;
			const UTF32 byteMark = 0x80;
			ch = *source++;

			if (flags == strictConversion)
			{
				/* UTF-16 surrogate values are illegal in UTF-32 */
				if (ch >= UNI_SUR_HIGH_START && ch <= UNI_SUR_LOW_END)
				{
					--source; /* return to the illegal value itself */
					result = sourceIllegal;
					break;
				}
			}

			/*
			 * Figure out how many bytes the result will require. Turn any
			 * illegally large UTF32 things (> Plane 17) into replacement chars.
			 */
			if (ch < (UTF32)0x80)
			{
				bytesToWrite = 1;

			}
			else if (ch < (UTF32)0x800)
			{
				bytesToWrite = 2;

			}
			else if (ch < (UTF32)0x10000)
			{
				bytesToWrite = 3;

			}
			else if (ch <= UNI_MAX_LEGAL_UTF32)
			{
				bytesToWrite = 4;

			}
			else
			{
				bytesToWrite = 3;
				ch = UNI_REPLACEMENT_CHAR;
				result = sourceIllegal;
			}

			target += bytesToWrite;

			if (target > targetEnd)
			{
				--source; /* Back up source pointer! */
				target -= bytesToWrite;
				result = targetExhausted;
				break;
			}

			switch (bytesToWrite)   /* note: everything falls through. */
			{
			case 4:
				*--target = (UTF8)((ch | byteMark) & byteMask);
				ch >>= 6;

			case 3:
				*--target = (UTF8)((ch | byteMark) & byteMask);
				ch >>= 6;

			case 2:
				*--target = (UTF8)((ch | byteMark) & byteMask);
				ch >>= 6;

			case 1:
				*--target = (UTF8)(ch | firstByteMark[bytesToWrite]);
			}

			target += bytesToWrite;
		}

		*sourceStart = source;
		*targetStart = target;
		return result;
	}

	/* --------------------------------------------------------------------- */

	ConversionResult ConvertUTF8toUTF32(
		const UTF8** sourceStart, const UTF8* sourceEnd,
		UTF32** targetStart, UTF32* targetEnd, ConversionFlags flags)
	{
		ConversionResult result = conversionOK;
		const UTF8* source = *sourceStart;
		UTF32* target = *targetStart;

		while (source < sourceEnd)
		{
			UTF32 ch = 0;
			unsigned short extraBytesToRead = trailingBytesForUTF8[*source];

			if (source + extraBytesToRead >= sourceEnd)
			{
				result = sourceExhausted;
				break;
			}

			/* Do this check whether lenient or strict */
			if (!isLegalUTF8(source, extraBytesToRead + 1))
			{
				result = sourceIllegal;
				break;
			}

			/*
			 * The cases all fall through. See "Note A" below.
			 */
			switch (extraBytesToRead)
			{
			case 5:
				ch += *source++;
				ch <<= 6;

			case 4:
				ch += *source++;
				ch <<= 6;

			case 3:
				ch += *source++;
				ch <<= 6;

			case 2:
				ch += *source++;
				ch <<= 6;

			case 1:
				ch += *source++;
				ch <<= 6;

			case 0:
				ch += *source++;
			}

			ch -= offsetsFromUTF8[extraBytesToRead];

			if (target >= targetEnd)
			{
				source -= (extraBytesToRead + 1); /* Back up the source pointer! */
				result = targetExhausted;
				break;
			}

			if (ch <= UNI_MAX_LEGAL_UTF32)
			{
				/*
				 * UTF-16 surrogate values are illegal in UTF-32, and anything
				 * over Plane 17 (> 0x10FFFF) is illegal.
				 */
				if (ch >= UNI_SUR_HIGH_START && ch <= UNI_SUR_LOW_END)
				{
					if (flags == strictConversion)
					{
						source -= (extraBytesToRead + 1); /* return to the illegal value itself */
						result = sourceIllegal;
						break;

					}
					else
					{
						*target++ = UNI_REPLACEMENT_CHAR;
					}
				}
				else
				{
					*target++ = ch;
				}
			}
			else     /* i.e., ch > UNI_MAX_LEGAL_UTF32 */
			{
				result = sourceIllegal;
				*target++ = UNI_REPLACEMENT_CHAR;
			}
		}

		*sourceStart = source;
		*targetStart = target;
		return result;
	}
}//namespace behaviac

/* ---------------------------------------------------------------------

	Note A.
	The fall-through switches in UTF-8 reading code save a
	temp variable, some decrements & conditionals.  The switches
	are equivalent to the following loop:
	{
	int tmpBytesToRead = extraBytesToRead+1;
	do {
	ch += *source++;
	--tmpBytesToRead;
	if (tmpBytesToRead) ch <<= 6;
	} while (tmpBytesToRead > 0);
	}
	In UTF-8 writing code, the switches on "bytesToWrite" are
	similarly unrolled loops.

	--------------------------------------------------------------------- */
